[Oyster_seed_group] August 28, 2011 Willapa Oyster Bulletin

From Alan Trimble

 Hello Everyone,
I am happy to say that the spatfall we were hoping for did actually happen. It was small, but occured throughout the southern reaches of the Bay. We placed three stacks of 11 Pacific Oyster shells at each of 16 sites on August 17 and retrieved them yesterday, August 27, and today. The shells were drilled to allow a 3/8″ dowel to pass through the middle and the shells were stacked smooth face down, with the dowel placed vertically in the sediment at approximately +1 ft above MLLW.
We counted spat on the smooth faces of all 528 shells and here are the results (# of spat per 11 shells):

Site                                    Stack 1                Stack 2                 Stack 3                Avg Spat/Shell
South Katzer                           4                       2                         2                            0.2
Long Isl Sl A                          16                     20                       20                            1.7
Long Isl Sl B                            9                      15                        8                            0.9
Chetlo Bank                            3                        0                        0                             0.1
Wilson Shack                        19                      13                        8                             1.2
Cougar Bend                         20                     29                       25                            2.2
Mill Ranch Rd                        15                     22                       16                            1.6
Mill Channel N                        6                     12                         8                            0.8
Mill Channel S                         9                       6                        8                             0.7
Peterson Channel                    4                       5                        4                             0.4
Peterson Hummock                11                    14                        3                             0.8
Smokey Entrance                     8                       4                      10                            0.6
Smokey Inside                         4                       5                        1                            0.3
Ivan’s Island                             7                      2                        4                            0.4
Bear River                              13                      5                       14                           1.0
Lewis Slough                         15                     26                      23                           1.9
Simple observations reveal that setting was slightly higher on the east side of Long Island than the west side. Also, Long Island Slough finally had a spatfall after many years without anything measurable. Also of interest is the difference in setting across opposite sides of the Naselle Channel (Lewis vs. South Katzer) and (Chetlo vs. Wilson.) Patterns like this are easy to observe but very difficult to explain.

We are continuing to track the younger larvae still swimming. As of Friday, here are the numbers for 1/2 of the samples. (we didn’t have time to count the other half and the shells at the same time…) Counts are per 20 gallons for the larger size classes (Early Umbo and Small Umbo, 80-180 microns).
There were also new straight hinge Paciic Larvae but those counts aren’t yet completed.

Site                     Count       Max Size
Lewis Slough         81         120
Long Isl Slough      30         150
Cougar Bend          72         160
Naselle Bridge       18         160
Mill Channel        110         120
Peterson Stn        108         120
Smokey Hollow    120         140
Bear River            111         140

My general impression is that the larvae closer to the ocean (mostly on the west side) are slowing down in growth rate and that the overall survival isn’t quite as good as the last cohort. The water temperatures are holding very close to “the same” for the past 2 weeks.

We will sample again tomorrow and hope for continued good news.

Regards,
Alan
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